linux-kernel - Re: [PATCH v3 2/6] mm/slab: Plumb kmem_buckets into __do_kmalloc

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Date: Fri, 31 May 2024 12:50:08 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Kees Cook <kees@...nel.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, Christoph Lameter <cl@...ux.com>, 
	Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, 
	Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org, 
	linux-hardening@...r.kernel.org, "GONG, Ruiqi" <gongruiqi@...weicloud.com>, 
	Xiu Jianfeng <xiujianfeng@...wei.com>, Suren Baghdasaryan <surenb@...gle.com>, 
	Jann Horn <jannh@...gle.com>, Matteo Rizzo <matteorizzo@...gle.com>, 
	Thomas Graf <tgraf@...g.ch>, Herbert Xu <herbert@...dor.apana.org.au>, 
	julien.voisin@...tri.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/6] mm/slab: Plumb kmem_buckets into
 __do_kmalloc_node()

On Fri, May 31, 2024 at 09:48:49AM -0700, Kees Cook wrote:
> On Fri, May 24, 2024 at 11:01:40AM -0400, Kent Overstreet wrote:
> > On Wed, Apr 24, 2024 at 02:40:59PM -0700, Kees Cook wrote:
> > > To be able to choose which buckets to allocate from, make the buckets
> > > available to the lower level kmalloc interfaces by adding them as the
> > > first argument. Where the bucket is not available, pass NULL, which means
> > > "use the default system kmalloc bucket set" (the prior existing behavior),
> > > as implemented in kmalloc_slab().
> > 
> > I thought the plan was to use codetags for this? That would obviate the
> > need for all this plumbing.
> > 
> > Add fields to the alloc tag for:
> >  - allocation size (or 0 if it's not a compile time constant)
> >  - union of kmem_cache, kmem_buckets, depending on whether the
> >    allocation size is constant or not
> 
> I want to provide "simple" (low-hanging fruit) coverage that can live
> separately from the codetags-based coverage. The memory overhead for
> this patch series is negligible, but I suspect the codetags expansion,
> while not giant, will be more than some deployments will want. I want
> to avoid an all-or-nothing solution -- which is why I had intended this
> to be available "by default".

You don't need to include the full codetag + alloc tag counters - with
the appropriate #ifdefs the overhead will be negligable.